1. Field of the Invention
This invention relates to removing residual toner from a toner transfer surface, and, more particularly to removing residual toner from a photoconductor surface of an electrophotographic printer.
2. Summary of the Background Information
FIG. 1 is a block diagram of a conventional electrophotographic printer 10, showing the major process stations arranged around a photoconductive element. For example, the photoconductive element comprises a photoconductive drum 12 having a peripheral surface 14 coated with a photoconductive material over an electrically grounded substrate, turning at a constant speed in the direction of arrow 16. Otherwise, a suitable photoconductive element may be a belt having an outer surface coated with a photoconductive material over an electrically conductive and grounded substrate.
The process of printing a document begins when an electrostatic charge is placed on the surface of the photoconductive drum 12 as it is moved past a charging station 18, which may include a number of wires extending adjacent to the surface of the drum 12, with the wires being held at an electrical potential sufficient to cause an electrical charge to be transferred to the surface of the drum 12. Next, at an exposure station 20, the surface of the electrophotographic drum 12 is exposed to an illuminated image that flows, or moves with the surface of the drum 12. For example, such an illuminated image may be produced by reflecting a modulated laser beam with a rotating mirror to repeatedly sweep across the surface of the photoconductive drum 12. The portions of the surface of the photoconductive drum 12 that are illuminated at the exposure station 18 become at least partially discharged, forming a latent image of charged and discharged areas, which is developed into a toned image as the surface of the photoconductive drum 12 is moved past a developing station 22, with its surface being exposed to electrically charged toner particles, which are preferentially attracted to either the charged or discharged areas of the surface of the drum 12 to form the toned image. For example, the electrostatic image may consist of discharged areas that are covered with toner particles while the adjacent undischarged areas remain essentially free of toner particles.
The toned image on the surface of the photoconductive drum 12 is then moved past a transfer station 24, in which toner from the toned image is transferred to a recording medium, such as a sheet of paper 26, which is moved into contact with the surface 14 of the rotating drum 12 at the transfer station 24. The transfer of the charged particles forming the toned image is generally aided by the application of an electric field between the surface of the photoconductive drum 12 and the side of the paper 24 opposite the surface moved against the drum 12. For example, a number of sheets of paper 24 may be fed in succession through the transfer station 22 to receive toned images generated in succession on the surface of the photoconductive drum 12. In general, some of the toner particles in the toned image are not transferred to the paper 24, leaving a residual image on the surface of the photoconductive drum 12. A cleaning station 28 is therefore provided to remove toner forming the residual image from the surface of the drum 12.
The electrophotographic printer 10 is an example of apparatus including a moving toner transfer surface, for example, the surface 14 of the photoconductive drum 12, on which a residual image is formed from which toner must be removed using a cleaning station. Such apparatus may be include a copying system in which a photoconductive surface is exposed to an image of an illuminated document formed by a lens. Otherwise, a moving toner transfer surface may be the surface of a drum on which images formed from differently colored toners are accumulated before a multi-colored image is transferred to a recording medium, such as a sheet of paper.
A number of types of electrophotographic printers use a rotating brush, such as a fur brush, engaging the photoconductive drum within the cleaning station 26 to remove toner particles from the toned image. For example, toner particles loosened from the surface of the drum 12 are removed by a vacuum system to be held within a filter through which air from the vacuum system is exhausted. A disadvantage of the use of a rotating brush arises from the fact that toner particles may agglomerate into larger particles or into a toner film, both of which are not readily removable by the rotating brush. An additional disadvantage of the use of a rotating brush within the cleaning station arises from the fact that large particles of agglomerated toner can become stuck within the rotating brush instead of being removed by the vacuum system. Some electrophotographic printers alleviate this problem by implementing a brush conditioning cycle at times when printing is not taking place. For example, after a predetermined distance of the surface of the photoconductive drum, such as 10,000 feet of surface a brush conditioning cycle is run when it is determined that a pause has occurred within the printing process. During the brush conditioning cycle, the photoconductive drum and the rotating brush are driven, with a housing extending around the rotating brush being moved to contact the brush. When the brush conditioning cycle is completed, the housing is returned to its normal position, and the electrophotographic printing process is allowed to resume.
Other types of electrophotographic printers employ a scraper blade held against the moving surface of a photoconductive drum or belt to remove toner from the residual image. The scraper blade is typically composed of a soft plastic or an elastomeric material. Disadvantages associated with this method include the fact that the surface of the photoconductive drum or belt may become scratched by contact stresses occurring during the scraping process, from the fact that the scraper blade may become ineffective due to wear occurring at its line of contact with the surface of the photoconductive drum or belt or due to the relaxation of stresses due to creep occurring within the scraper blade. A further disadvantage arises from the fact that toner may become attached to the surface of the scraper blade.
The patent literature includes a number of descriptions of photoconductor cleaning stations including both a rotating brush and a scraper blade held against the photoconductor surface in a position following the brush. For example, U.S. Pat. No. 5,832,355 describes such a cleaning station having a stripper, or scraper blade composed of an abrasion-resistant plastic. U.S. Pat. No. 5,339,140 describes a photoconductor cleaning station having a pair of rotating brushes and a spots cleaning blade to remove residual agglomerations of particles from the imaging surface. The spots cleaning blade is made from a material, such as a urethane or polyester material, that has a low coefficient of friction compared to the soft plastic and elastomeric material previously used for photoconductor scraper blades. U.S. Pat. Nos. 4,989,047 and 5,031,000 describe the use of a secondary cleaning member, in the form of a thin scraper blade, used in association with a primary cleaning member in the form of a rotating brush, with the scraper blade being additionally characterized as having a low angle of attack with the photoconductor surface or as being loaded by means of a weight against the photoconductor surface. U.S. Pat. Nos. 4,984,028 and 5,066,983 describe a cleaning station including a rotating brush and a scraper blade disposed immediately following the brush, with toner being evacuated from the cleaning station by air sucked through a filter and an air pump from a housing structure surrounding the blade and the rotating brush. The cleaning station of U.S. Pat. No. 5,066,983 is further characterized by the continuous removal of larger particles of contamination accumulated and the cleaning edge of the blade by the rotating brush, while the smaller particles of contaminants serve to lubricate the area between the cleaning blade and the surface of the photoconductive drum. U.S. Pat. No. 4,451,139 describes a cleaning station including a rotating brush, a scraper blade, and a housing having provisions for removing the cleaning station without damaging the photoconductive surface.
Other patents, such as U.S. Pat. No. 4,640,608, describe photoconductor cleaning stations including both a rotating brush and a scraper blade that is moved into contact with the photoconductive drum as the rotation of the photoconductive drum is begun, or as the process of printing or copying a document is started, and that is moved out of contact with the photoconductive drum as the rotation of the drum is stopped, or as the process of printing or copying a document is completed.
U.S. Pat. No. 5,442,422 describes a cleaning station including a rotating brush, a scraper blade that is moved into, and out of, contact, and an additional sealing strip, disposed below the cleaning blade, that is moved into, and out of contact with the photoconductor. In particular, when the cleaning station is to be removed from the system for service with the scraper blade out of contact with the photoconductor, the sealing strip is first moved into contact with the photoconductor to prevent contamination of the system with residual toner from the cleaning station. U.S. Pat. No. 4,969,015 and Japanese Patent Application 60-083981 describe such a cleaning station including an additional scraper blade held against the side of the scraper blade as it is moved away from the photoconductor to remove deposits from the scraper blade that is used to clean the photoconductor.
U.S. Pat. No. 5,083,169 describes a cleaning station without a scraper blade, in which a fur brush mounted on a pivot arm is moved into contact with the photoconductor each time a predetermined number of copies of a document have been printed and after the copier is turned off.
The patent literature additionally includes descriptions of cleaning stations using scraper blades without associated rotating brushes. For example, U.S. Patent App. Pub. 2004/0136763 A1 describes a cleaning unit including first and second scraper blades, with the first blade removing adhered substances and with the second blade, following the first blade, having an abrasive layer that is formed by including abrasive particles within an elastic material. U.S. Pat. No. 5,053,827 describes a scraper blade that is moved into contact with a surface carrying a residual image only during the passage of the residual image when it needs to be removed. U.S. Pat. No. 6,697,599 describes a scraper blade that is supported in a region where it is bent to be held against the photoconductor at a leading edge of the scraper blade and additionally adjacent the bend region.